1. Field of the Invention
The present invention relates to a method and apparatus for making a flat wiring harness which can make effective use of narrow automotive space.
2. Description of the Prior Art
Flat wiring harnesses generally have a construction, as shown in FIG. 17a, in which a plurality of covered wires a are parallelly arranged and secured together like a flat plate.
Such a straight wiring harness, however, is not practical. Actual installation situations often require, as shown in FIG. 17b, that the wiring harness have a trunk portion b and a plurality of branches c1, c2, . . . shooting out from the trunk and that these groups of wires be formed into various shapes such as curves, L and Y shapes. In other words, the wiring harness must have a two-dimensional shape that fits into the complex shape of space in the automobiles.
The following two facts ma be cited as the reasons that the conventional flat wiring harnesses have failed to find general use.
(1) It has been difficult to lay a large number of twisted wires in a parallel arrangement and keep them in a desired two-dimensional pattern of wiring harness.
(2) There has been no established technique to bond together a group of wires in a particular shape at low cost, easily and reliably.
In a conventional method of arranging a plurality of wires in parallel like a flat plate, the following process has been taken. As shown in FIG. 18a, alignment guides f are positioned at both ends of a wire arrangement table d with an opening e cut between the ends. Then wires a are passed through the guides f one at a time (Japanese Patent Application Kokai Publication No. 122309/1980).
With this method, however, gaps are formed between the wires by the guides f. And when the arranged wires are secured together by insulating tapes q as shown in FIG. 18b, the product's width becomes inevitably large. This runs counter to the demands for smaller size.
There are very few reports published so far regarding a flat wiring harness, which consists of a plurality of parallel wires bonded together that are formed into a desired two-dimensional pattern corresponding to the shape of the automotive space. One example available is the Japanese Utility Model Reg. Application Kokai Publication No. 72189/1978, in which as shown in FIG. 19a wires a are laid parallel on a back member (vinyl sheet) i one wire at a time and then hot air is blown to fuse them together.
Other methods of bonding wires together, in addition to the one shown in FIG. 19a, are illustrated in FIGS. 19b to 19d. FIG. 19b represents a method in which upper and lower dies j, k are used to mold the wires together using resin (Japanese Patent Application Kokai Publication No. 55789/1978); FIG. 19c illustrates a method in which adhesive is applied from the orifice m of nozzle l onto the wires a (Japanese Patent Application Kokai Publication No. 16211/1984); and FIG. 19d shows a method in which a group of wires a are secured together by fiber materials n, n', in a plate-like form (Japanese Patent Application Kokai Publication No. 34808/1988).
The methods shown in FIGS. 19a to 19d, however, tend to increase the complexity of the apparatus and therefore the cost. They are also restricted in application to only simple configurations of wiring harness such as straight line, and with these methods it is very difficult to form curved or branched harnesses.